"Robotic" is quite an abstract, poorly defined, and ambiguous term. Robots (in the literal sense) are deterministic and task orientated. A machine does not deal with the finer tangential abstractions, ponder away at its own thoughts, or constantly question its own programming. It's worth noting the diversity amongst individuals of any type; to what extent are generalisations too broad.
INTJs appear more extroverted, verbal, and 'human' than INTPs, but I think they are more robotic in nature. INTJs tend to prefer order, planning, and structure, they will organise themselves and be quite diligent at following their plans, acting in accordance with a 'script', and generally are much more immersed in external activities. INTPs go with the flow, procrastinate, and usually perform tasks in random spurts of motivation as opposed to diligent planning.
Secondly, INTPs are not as dogmatically confident of their own opinions/cognitions, always questioning, and may even change their opinion on something in the midst of arguing in support of it. INTJs do not usually question their own opinions in an argument. They favour an 'algorithmic' approach to beating their opponent. An opinionated INTJ is robotic in that sense, 'they are right', and they will always seek to affirm this, generally in a predictable manner. The argument is just a means to an end, to 'win', to affirm their opinion. INTPs in argument value the aesthetic value of the argument itself, as they seek to learn new perspectives from it, and may form new connections.
I'm starting to waffle, so will summarise:
INTPs often appear very robotic and computer like, but their internal cognitions are very abstract, imaginative, capacious, examining a whole manner of ideas to filter out the logical from the spurious. INTJs are more concrete, they have their interests and views, and focus around them. INTPs are often, for lack of better word, lazy, in the external world at least, because their internal world can overshadow the external.
Robots are not lazy.
